Magnetoresistive random access memory

ABSTRACT

A semiconductor device includes: a substrate comprising a magnetic tunneling junction (MTJ) region and a logic region; a first MTJ on the MTJ region; a first metal interconnection on the logic region; and a cap layer extending from a sidewall of the first MTJ to a sidewall of the first metal interconnection. Preferably, the cap layer on the MTJ region and the cap layer on the logic region comprise different thicknesses.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.16/589,083, filed on Sep. 30, 2019, and all benefits of such earlierapplication are hereby claimed for this new continuation application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention relates to a semiconductor device, and more particularly,to a magnetoresistive random access memory (MRAM).

2. Description of the Prior Art

Magnetoresistance (MR) effect has been known as a kind of effect causedby altering the resistance of a material through variation of outsidemagnetic field. The physical definition of such effect is defined as avariation in resistance obtained by dividing a difference in resistanceunder no magnetic interference by the original resistance. Currently, MReffect has been successfully utilized in production of hard disksthereby having important commercial values. Moreover, thecharacterization of utilizing GMR materials to generate differentresistance under different magnetized states could also be used tofabricate MRAM devices, which typically has the advantage of keepingstored data even when the device is not connected to an electricalsource.

The aforementioned MR effect has also been used in magnetic field sensorareas including but not limited to for example electronic compasscomponents used in global positioning system (GPS) of cellular phonesfor providing information regarding moving location to users. Currently,various magnetic field sensor technologies such as anisotropicmagnetoresistance (AMR) sensors, GMR sensors, magnetic tunnelingjunction (MTJ) sensors have been widely developed in the market.Nevertheless, most of these products still pose numerous shortcomingssuch as high chip area, high cost, high power consumption, limitedsensibility, and easily affected by temperature variation and how tocome up with an improved device to resolve these issues has become animportant task in this field.

SUMMARY OF THE INVENTION

According to an embodiment of the present invention, a semiconductordevice includes: a substrate comprising a magnetic tunneling junction(MTJ) region and a logic region; a first MTJ on the MTJ region; a firstmetal interconnection on the logic region; and a cap layer extendingfrom a sidewall of the first MTJ to a sidewall of the first metalinterconnection. Preferably, the cap layer on the MTJ region and the caplayer on the logic region comprise different thicknesses.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-7 illustrate a method for fabricating a semiconductor deviceaccording to an embodiment of the present invention.

FIGS. 8-9 illustrate a method for fabricating semiconductor deviceaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

Referring to FIGS. 1-7, FIGS. 1-7 illustrate a method for fabricating asemiconductor device, or more specifically a MRAM device according to anembodiment of the present invention. As shown in FIG. 1, a substrate 12made of semiconductor material is first provided, in which thesemiconductor material could be selected from the group consisting ofsilicon (Si), germanium (Ge), Si—Ge compounds, silicon carbide (SiC),and gallium arsenide (GaAs), and a MTJ region 14 and a logic region 16are defined on the substrate 12.

Active devices such as metal-oxide semiconductor (MOS) transistors,passive devices, conductive layers, and interlayer dielectric (ILD)layer 18 could also be formed on top of the substrate 12. Morespecifically, planar MOS transistors or non-planar (such as FinFETs) MOStransistors could be formed on the substrate 12, in which the MOStransistors could include transistor elements such as gate structures(for example metal gates) and source/drain region, spacer, epitaxiallayer, and contact etch stop layer (CESL). The ILD layer 18 could beformed on the substrate 12 to cover the MOS transistors, and a pluralityof contact plugs could be formed in the ILD layer 18 to electricallyconnect to the gate structure and/or source/drain region of MOStransistors. Since the fabrication of planar or non-planar transistorsand ILD layer is well known to those skilled in the art, the details ofwhich are not explained herein for the sake of brevity.

Next, metal interconnect structures 20, 22 are sequentially formed onthe ILD layer 18 on the MTJ region 14 and the edge region 16 toelectrically connect the aforementioned contact plugs, in which themetal interconnect structure 20 includes an inter-metal dielectric (IMD)layer 24 and metal interconnections 26 embedded in the IMD layer 24, andthe metal interconnect structure 22 includes a stop layer 28, an IMDlayer 30, and metal interconnections 32 embedded in the stop layer 28and the IMD layer 30.

In this embodiment, each of the metal interconnections 26 from the metalinterconnect structure 20 preferably includes a trench conductor andeach of the metal interconnections 32 from the metal interconnectstructure 22 on the MTJ region 14 includes a via conductor. Preferably,each of the metal interconnections 26, 32 from the metal interconnectstructures 20, 22 could be embedded within the IMD layers 24, 30 and/orstop layer 28 according to a single damascene process or dual damasceneprocess. For instance, each of the metal interconnections 26, 32 couldfurther includes a barrier layer 34 and a metal layer 36, in which thebarrier layer 34 could be selected from the group consisting of titanium(Ti), titanium nitride (TiN), tantalum (Ta), and tantalum nitride (TaN)and the metal layer 36 could be selected from the group consisting oftungsten (W), copper (Cu), aluminum (Al), titanium aluminide (TiAl), andcobalt tungsten phosphide (CoWP). Since single damascene process anddual damascene process are well known to those skilled in the art, thedetails of which are not explained herein for the sake of brevity. Inthis embodiment, the metal layers 36 are preferably made of copper, theIMD layers 24, 30 are preferably made of silicon oxide, and the stoplayers 28 is preferably made of nitrogen doped carbide (NDC), siliconnitride, silicon carbon nitride (SiCN), or combination thereof.

Next, a MTJ stack 38 or stack structure is formed on the metalinterconnect structure 22, a cap layer 40 is formed on the MTJ stack 38,and another cap layer 42 formed on the cap layer 40. In this embodiment,the formation of the MTJ stack 38 could be accomplished by sequentiallydepositing a first electrode layer 44, a fixed layer 46, a barrier layer48, a free layer 50, and a second electrode layer 52 on the IMD layer30. In this embodiment, the first electrode layer 44 and the secondelectrode layer 52 are preferably made of conductive material includingbut not limited to for example Ta, Pt, Cu, Au, Al, or combinationthereof. The fixed layer 46 could be made of antiferromagnetic (AFM)material including but not limited to for example ferromanganese (FeMn),platinum manganese (PtMn), iridium manganese (IrMn), nickel oxide (NiO),or combination thereof, in which the fixed layer 46 is formed to fix orlimit the direction of magnetic moment of adjacent layers. The barrierlayer 48 could be made of insulating material including but not limitedto for example oxides such as aluminum oxide (AlO_(x)) or magnesiumoxide (MgO). The free layer 50 could be made of ferromagnetic materialincluding but not limited to for example iron, cobalt, nickel, or alloysthereof such as cobalt-iron-boron (CoFeB), in which the magnetizeddirection of the free layer 50 could be altered freely depending on theinfluence of outside magnetic field. Preferably, the cap layer 40 andcap layer 42 are made of different materials. For instance, the caplayer 40 is preferably made of silicon nitride and the cap layer 42 ismade of silicon oxide, but not limited thereto.

Next, a patterned mask 54 is formed on the cap layer 42. In thisembodiment, the patterned mask 54 could include an organic dielectriclayer (ODL) 56, a silicon-containing hard mask bottom anti-reflectivecoating (SHB) 58, and a patterned resist 60.

Next, as shown in FIG. 2, one or more etching process is conducted byusing the patterned mask 54 as mask to remove part of the cap layers 40,42, part of the MTJ stack 38, and part of the IMD layer 30 to form MTJ62 and MTJ 72 on the MTJ region 14, in which the first electrode layer44 at this stage preferably becomes a bottom electrode 76 for the MTJs62, 72 while the second electrode layer 52 becomes a top electrode 78for the MTJs 62, 72 and the cap layers 40, 42 could be removed duringthe etching process. It should be noted that this embodiment preferablyconducts a reactive ion etching (RIE) process by using the patternedmask 54 as mask to remove part of the cap layers 40, 42 and part of theMTJ stack 38, strips the patterned mask 54, and then conducts an ionbeam etching (IBE) process by using the patterned cap layer 42 as maskto remove part of the MTJ stack 38 and part of the IMD layer 30 to formMTJs 62, 72. Due to the characteristics of the IBE process, the topsurface of the remaining IMD layer 30 is slightly lower than the topsurface of the metal interconnections 32 after the IBE process and thetop surface of the IMD layer 30 also reveals a curve or an arc.

It should also be noted that when the IBE process is conducted to removepart of the IMD layer 30, part of the metal interconnections 32 areremoved at the same time so that a first slanted sidewall 64 and asecond slanted sidewall 66 are formed on the metal interconnections 32adjacent to the MTJ 62, in which each of the first slanted sidewall 64and the second slanted sidewall 66 could further include a curve (orcurved surface) or a planar surface.

Next, as shown in FIG. 3, a cap layer 68 is formed on the MTJ 62, 72 tocover the surface of the IMD layer 30. In this embodiment, the cap layer68 is preferably made of silicon nitride, but could also be made ofother dielectric material including but not limited to for examplesilicon oxide, silicon oxynitride, or silicon carbon nitride.

Next, as shown in FIG. 4, an atomic layer deposition (ALD) process isconducted to form a passivation layer 80 on the surface of the cap layer68 to fully cover the MTJs 62, 72, in which the passivation layer 80preferably includes silicon oxide and the topmost surface of thepassivation layer 80 is higher than the top surface of the topelectrodes 78. It should be noted that the cap layer 68 disposed on boththe MTJ region 14 and logic region 16 at this stage still has an eventhickness or that the thickness of the cap layer 68 on the MTJ region 14is equal to the thickness of the cap layer 68 on the logic region 16.

Next, as shown in FIG. 5, an etching back process is conducted to removepart of the passivation layer 80 and even part of the cap layer 68 sothat the top surface of the remaining passivation layer 80 is even withthe top surface of the remaining cap layer 68. Specifically, an etchingprocess is conducted by using the selectivity between the passivationlayer 80 and cap layer 68 without forming any patterned mask at thisstage to remove part of the passivation layer 80 and part of the caplayer 68, in which the passivation layer 80 being removed includes partof the passivation layer 80 on both MTJ region 14 and logic region 16while the cap layer 68 being removed includes part of the cap layer 68directly on top of the top electrodes 78 and part of the cap layer 68 onthe logic region 16 excepting part of the cap layer 68 between the MTJs62, 72. Since some of the cap layer 68 on the MTJ region 14 is removedduring the etching process while some of the cap layer 68 on the sameregion 14 is not removed, the remaining cap layer 68 after the etchingprocess preferably includes at least two thicknesses. For instance, thethinnest portion of the cap layer 68 adjacent to two sides of theremaining passivation layer 80 on the logic region 16 includes a firstthickness T1, the cap layer 68 directly on top of the top electrodes 78includes a second thickness T2, and the cap layer 68 between the MTJs62, 72 includes a third thickness T3. Specifically, the first thicknessT1 could be the same as or different from the second thickness T2, whileeach of the first thickness T1 and the second thickness T2 is less thanthe third thickness T3, in which each of the first thickness T1 and/orthe second thickness T2 is preferably between 50-150 Angstroms and thethird thickness T3 is between 50-250 Angstroms.

It should also be noted that after part of the passivation layer 80 isremoved by the aforementioned etching back process the remainingpassivation layer 80 still surrounds the MTJs 62, 72, in which the topsurface of the passivation layer 80 between the MTJs 62, 72 preferablyincludes a V-shape, the V-shape is lower than the top surface of the topelectrodes 78, and the angle included by the V-shape is greater than 100degrees but could also be less than 100 degrees depending on the demandof the process.

Next, as shown in FIG. 6, another IMD layer 82 is formed on the MTJregion 14 and logic region 16, and a planarizing process such as CMP isconducted to remove part of the IMD layer 82 so that the top surface ofthe IMD layer 82 is even with the top surface of the passivation layer80. Next, a pattern transfer process is conducted by using a patternedmask (not shown) to remove part of the IMD layer 82, part of the caplayer 68, part of the IMD layer 30, and part of the stop layer 28 on thelogic region 16 to form a contact hole (not shown) exposing the metalinterconnection 26 underneath and conductive materials are depositedinto the contact hole afterwards. For instance, a barrier layer selectedfrom the group consisting of titanium (T1), titanium nitride (TiN),tantalum (Ta), and tantalum nitride (TaN) and metal layer selected fromthe group consisting of tungsten (W), copper (Cu), aluminum (Al),titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP) could bedeposited into the contact hole, and a planarizing process such as CMPcould be conducted to remove part of the conductive materials includingthe aforementioned barrier layer and metal layer to form a contact plugor metal interconnection 84 in the contact hole electrically connectingthe metal interconnection 26.

Next, as shown in FIG. 7, a stop layer 86 and another IMD layer 88 areformed on the MTJs 62, 72 to cover the surface of the IMD layer 82, andone or more photo-etching process is conducted to remove part of the IMDlayer 88, part of the stop layer 86, and even part of the cap layer 68on the MTJ region 14 and part of the IMD layer 88 and part of the stoplayer 86 on the logic region 16 to form contact holes (not shown). Next,conductive materials are deposited into each of the contact holes and aplanarizing process such as CMP is conducted to form metalinterconnections 90, 92 directly connecting the top electrodes 78 andmetal interconnection 84 underneath, in which the metal interconnection90 on the MTJ region 14 directly contacts the top electrodes 78underneath while the metal interconnection 92 on the logic region 16directly contacts the metal interconnection 84 on the lower level. Next,another stop layer 94 is formed on the IMD layer 88 to cover the metalinterconnections 90, 92.

In this embodiment, the stop layer 86 and the stop layer 28 could bemade of same material or different material. For example, both layers82, 28 could include nitrogen doped carbide (NDC), silicon nitride,silicon carbon nitride (SiCN), or combination thereof. Similar to themetal interconnections formed previously, each of the metalinterconnections 90, 92 could be formed in the IMD layer 88 through asingle damascene or dual damascene process. For instance, each of themetal interconnections 90, 92 could further include a barrier layer anda metal layer, in which the barrier layer could be selected from thegroup consisting of titanium (Ti), titanium nitride (TiN), tantalum(Ta), and tantalum nitride (TaN) and the metal layer could be selectedfrom the group consisting of tungsten (W), copper (Cu), aluminum (Al),titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP). Sincesingle damascene process and dual damascene process are well known tothose skilled in the art, the details of which are not explained hereinfor the sake of brevity. This completes the fabrication of asemiconductor device according to an embodiment of the presentinvention.

Referring to FIG. 7, FIG. 7 further illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 7, the semiconductor device preferablyincludes MTJs 62, 72 disposed on the MTJ region 14, a metalinterconnection 84 disposed on the logic region 16, metalinterconnections 32 disposed directly under the MTJs 62, 72, an IMDlayer 30 disposed around the metal interconnections 32, a cap layer 68extending from on a sidewall of the MTJ 72 to a sidewall of the metalinterconnection 84, a passivation layer 80 on the cap layer 68 andsurrounding the MTJs 62, 72, an IMD layer 82 disposed on the cap layer68 and surround the passivation layer 80, another IMD layer 88 disposedon the IMD layer 82, and metal interconnections 90, 92 disposed in theIMD layer 88 to electrically connect the top electrodes 78 and metalinterconnection 84 underneath.

In this embodiment, the cap layer 68 disposed on the MTJ region 14 andthe cap layer 68 disposed on the logic region 16 preferably includesdifferent thicknesses, or more specifically a thickness of the cap layer68 disposed on the IMD layer 30 on the logic region 16 is preferablyless than a thickness of the cap layer 68 disposed on the IMD layer 30between the MTJs 62, 72. Viewing from a more detailed perspective, thethinnest portion of the cap layer 68 adjacent to two sides of thepassivation layer 80 on the logic region 16 includes a first thicknessT1, the cap layer 68 directly on top of the top electrodes 78 includes asecond thickness T2, and the cap layer 68 on sidewalls of the MTJs 62,72 and/or the cap layer 68 directly on top of the IMD layer 30 betweenthe MTJs 62, 72 includes a third thickness T3, in which the firstthickness T1 could be the same as or different from the second thicknessT2 while each of the first thickness T1 and the second thickness T2 isless than the third thickness T3. In this embodiment, each of the firstthickness T1 and/or the second thickness T2 is preferably between 50-150Angstroms and the third thickness T3 is between 50-250 Angstroms.Moreover, the top surfaces of the IMD layer 32, passivation layer 80,cap layer 68, and metal interconnection 84 are coplanar and thepassivation layer 80 and IMD layer 82 are preferably made of differentmaterials, in which the passivation layer 80 preferably includes whilethe IMD layer 82 could include a ultra low-k (ULK) dielectric layer suchas porous dielectric materials including but not limited to for examplesilicon oxycarbide (SiOC).

Referring to FIGS. 8-9, FIGS. 8-9 illustrate a method for fabricatingsemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 8, it would be desirable to first conductthe aforementioned process in FIGS. 1-5 by using an etching back processto remove part of the passivation layer 80 so that the top surface ofthe remaining passivation layer 80 is even with the top surface of thecap layer 68, form an IMD layer 82 on the MTJ region 14 and logic region16, and then conduct a planarizing process such as CMP to remove part ofthe IMD layer 82. It should be noted that in contrast to conduct the CMPprocess in FIG. 6 for removing part of the IMD layer 82 so that the topsurface of the remaining IMD layer 82 is substantially even with the topsurfaces of the passivation layer 80 and cap layer 68, the presentembodiment preferably conducts the CMP process to remove part of the IMDlayer 82 while controlling the remaining heights between the IMD layer82 and the passivation layer 80 so that the top surface of the IMD layer82 is slightly higher than the top surfaces of the passivation layer 80and the cap layer 68.

Next, a pattern transfer process is conducted by using a patterned mask(not shown) to remove part of the IMD layer 82, part of the cap layer68, part of the IMD layer 30, and part of the stop layer 28 on the logicregion 16 to form a contact hole (not shown) exposing the metalinterconnection 26 underneath and conductive materials are depositedinto the contact hole afterwards. For instance, a barrier layer selectedfrom the group consisting of titanium (Ti), titanium nitride (TiN),tantalum (Ta), and tantalum nitride (TaN) and metal layer selected fromthe group consisting of tungsten (W), copper (Cu), aluminum (Al),titanium aluminide (TiAl), and cobalt tungsten phosphide (CoWP) could bedeposited into the contact hole, and a planarizing process such as CMPcould be conducted to remove part of the conductive materials includingthe aforementioned barrier layer and metal layer to form a contact plugor metal interconnection 84 in the contact hole electrically connectingthe metal interconnection 26.

Next, as shown in FIG. 9, a stop layer 86 and another IMD layer 88 areformed on the MTJs 62, 72 to cover the surface of the IMD layer 82, andone or more photo-etching process is conducted to remove part of the IMDlayer 88, part of the stop layer 86, and even part of the cap layer 68on the MTJ region 14 and part of the IMD layer 88 and part of the stoplayer 86 on the logic region 16 to form contact holes (not shown). Next,conductive materials are deposited into each of the contact holes and aplanarizing process such as CMP is conducted to form metalinterconnections 90, 92 directly connecting the top electrodes 78 andmetal interconnection 84 underneath, in which the metal interconnection90 on the MTJ region 14 directly contacts the top electrodes 78underneath while the metal interconnection 92 on the logic region 16directly contacts the metal interconnection 84 on the lower level. Next,another stop layer 94 is formed on the IMD layer 88 to cover the metalinterconnections 90, 92.

Referring to FIG. 9, FIG. 9 further illustrates a structural view of asemiconductor device according to an embodiment of the presentinvention. As shown in FIG. 9, the semiconductor device preferablyincludes MTJs 62, 72 disposed on the MTJ region 14, a metalinterconnection 84 disposed on the logic region 16, metalinterconnections 32 disposed directly under the MTJs 62, 72, an IMDlayer 30 disposed around the metal interconnections 32, a cap layer 68extending from on a sidewall of the MTJ 72 to a sidewall of the metalinterconnection 84, a passivation layer 80 on the cap layer 68 andsurrounding the MTJs 62, 72, an IMD layer 82 disposed on the cap layer68 and surround the passivation layer 80, another IMD layer 88 disposedon the IMD layer 82, and metal interconnections 90, 92 disposed in theIMD layer 88 to electrically connect the top electrodes 78 and metalinterconnection 84 underneath.

In this embodiment, the top surface of the IMD layer 82 is even with thetop surface of the metal interconnection 84, the top surface of the caplayer 68 directly on top of the electrodes 78 is lower than the topsurface of the IMD layer 82, the top surface of the passivation layer 80is lower than the top surface of the IMD layer 82, the top surfaces ofthe cap layer 68 and passivation layer 80 are coplanar, and the IMDlayer 82 contacts the top surfaces of the cap layer 68 and passivationlayer 80 directly.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

What is claimed is:
 1. A semiconductor device, comprising: a substratecomprising a magnetic tunneling junction (MTJ) region and a logicregion; a first MTJ on the MTJ region; a first metal interconnection onthe logic region; and a cap layer extending from a sidewall of the firstMTJ to a sidewall of the first metal interconnection, wherein the caplayer on the MTJ region and the cap layer on the logic region comprisedifferent thicknesses.
 2. The semiconductor device of claim 1, furthercomprising: a first inter-metal dielectric (IMD) layer on the substrate;a second metal interconnection and a third metal interconnection on theMTJ region, wherein the first MTJ is on the second metal interconnectionand a second MTJ is on the third metal interconnection.
 3. Thesemiconductor device of claim 2, wherein the cap layer on the first IMDlayer between the first MTJ and the second MTJ and the cap layer on thelogic region comprise different thicknesses.
 4. The semiconductor deviceof claim 3, wherein a thickness of the cap layer on the first IMD layeron the logic region is less than a thickness of the cap layer on thefirst IMD layer between the first MTJ and the second MTJ.
 5. Thesemiconductor device of claim 2, further comprising a passivation layeron the MTJ region between the first MTJ and the second MTJ.
 6. Thesemiconductor device of claim 5, wherein the passivation layer betweenthe first MTJ and the second MTJ comprises a V-shape.
 7. Thesemiconductor device of claim 5, further comprising a second IMD layeron the cap layer around the passivation layer.
 8. The semiconductordevice of claim 7, wherein top surfaces of the second IMD layer and thepassivation layer are coplanar.
 9. The semiconductor device of claim 7,wherein top surfaces of the second IMD layer and the first metalinterconnection are coplanar.
 10. The semiconductor device of claim 1,wherein a thickness of the cap layer on the logic region is less than athickness of the cap layer on the MTJ region.